Answer: 20 cm
Step-by-step explanation: Isolate the variable by dividing each side by factors that don't contain a variable.
Step by step explanation:
X + y=25
-y. -y
X=25-y
3x +4y= 90
3(25-y) =90
75-3y=90
-75. -75
-3y =15
/-3. /-3
Y=-5
X=25-(-5)
X= 25+5
X=30
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Recall that the quadratic formula is
x=(-b+/-sqrt(b^2-4ac)/2a
So the formula cannot be used whenever a=0, in other words, the coefficient of the x^2 term is zero. All other situations do not render the formula inapplicable.